While the present invention was developed for use in connection with hydraulic steering systems used on underground loaders, i.e., loaders used to load minerals and ores in underground mines, and as described in combination with an underground loader hydraulic steering mechanism, it is to be understood that the invention can also be utilized in other types of hydraulic control systems, particularly hydraulic control systems that respond to manual inputs applied via a control valve.
The type of underground loader that the invention was developed to be used with includes a forward section and an aft section hinged together about a vertical axis. The forward section supports a pair of forward wheels and the rear of aft section supports a pair of rear wheels. Steering is accomplished by a pair of hydraulic actuators mounted between the fore and aft sections of the loader. The hydraulic actuators are located on opposite sides of the hinge axis. Steering is accomplished by extending the rod of one of the hydraulic actuators and retracting the rod of the other hydraulic actuator to cause a rotation of one section of the loader with respect to the other section, about the vertical hinge axis. As a result, a greater displacement is created between the wheels located on one side of the loader and the wheels located on the other side, causing the underground loader to turn when power is applied to the drive wheels.
In the past, underground loader hydraulic steering systems have been manually controlled by an operator moving a lever arm that controls the position of the piston of a bidirectional, spring-loaded hydraulic control valve. When the lever is pulled in one direction, hydraulic fluid pressure is applied to the chamber on one side of the piston of one of the hydraulic steering actuators and to the chamber on the other side of the piston of the other steering actuator. Further, the manually controlled valve opens a pathway for fluid located in the nonpressurized chambers of the hydraulic actuators to flow to a hydraulic fluid reservoir, i.e., a tank. Movement of the lever arm in the opposite direction causes the opposite result, i.e., the manually actuated hydraulic control valve applies hydraulic fluid pressure to the chambers located on the previously unpressurized sides of the pistons of the hydraulic steering actuators and opens a pathway for fluid located in the previously pressurized chambers to return to the tank. In most cases, pressure relief valves are mounted between the lines running from the manually actuated hydraulic control valve to the steering hydraulic actuators to prevent the application of excessive pressure to the hydraulic steering actuator chambers.
In recent years, attempts have been made to remotely control the steering of underground loaders. In most instances, the attempts have focused on providing a remote control system for controlling the position of the lever arm moved by the operator to provide manual steering control. Unfortunately, these attempts have not been as successful as desired. This is primarily due to the fact that loaders are operated at idle, full speed, or half speed. In-between speeds are not available. Remote control systems designed to control the position of the hydraulic control valve used for manual control have proven to be inadequate because they are unable to respond quickly enough to prevent loader over and understeering. Over and understeering can result in loaders slamming into nearby objects, which is destructive to equipment as well as dangerous to nearby personnel. The present invention is directed to providing a remote control modification that is responsive enotgh to greatly diminish, if not completely avoid, this problem.